Nano Research
Nano Res
DOI 10.1007/s12274-015-0873-0
Hydrogenation of molecular oxygen to hydroperoxyl:
An alternative pathway for O2 activation on nanogold
catalysts
Chun-Ran Chang1,2 (), Zheng-Qing, Huang1, and Jun Li2 ()
Nano Res., Just Accepted Manuscript • DOI 10.1007/s12274-015-0873-0
http://www.thenanoresearch.com on August 4, 2015
© Tsinghua University Press 2015
Just Accepted
This is a “Just Accepted” manuscript, which has been examined by the peer-review process and has been
accepted for publication. A “Just Accepted” manuscript is published online shortly after its acceptance,
which is prior to technical editing and formatting and author proofing. Tsinghua University Press (TUP)
provides “Just Accepted” as an optional and free service which allows authors to make their results available
to the research community as soon as possible after acceptance. After a manuscript has been technically
edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP
article. Please note that technical editing may introduce minor changes to the manuscript text and/or
graphics which may affect the content, and all legal disclaimers that apply to the journal pertain. In no event
shall TUP be held responsible for errors or consequences arising from the use of any information contained
in these “Just Accepted” manuscripts. To cite this manuscript please use its Digital Object Identifier (DOI® ),
which is identical for all formats of publication.
1
TABLE OF CONTENTS (TOC)
Hydrogenation of Molecular Oxygen to Hydroperoxyl:
An Alternative Pathway for O2 Activation on Nanogold
Catalysts
Chun-Ran Chang1,2*, Zheng-Qing, Huang1, and Jun Li2*
1
School of Chemical Engineering and Technology, Xi’an
Jiaotong University, Xi’an 710049, China
2
Department of Chemistry and Key Laboratory of
Organic Optoelectronics and Molecular Engineering of
Ministry of Education, Tsinghua University, Beijing
100084, China
We report that molecular oxygen (dioxygen) can be feasibly
activated through a hydroperoxyl (OOH) radical species by
abstracting a hydrogen atom from H-containing coadsorbates
on Au nanoparticles. The formed OOH oxidant either directly
undergoes oxidation reactions through the end-on oxygen atom
or dissociates into atomic oxygen and hydroxyl for further
oxidation.
Nano Research
DOI (automatically inserted by the publisher)
Research Article
Hydrogenation of Molecular Oxygen to Hydroperoxyl:
An Alternative Pathway for O2 Activation on Nanogold
Catalysts
Chun-Ran Chang1,2 (), Zheng-Qing, Huang1, and Jun Li2 ()
Received: day month year
ABSTRACT
Revised: day month year
Activation of molecular O2 is the most critical step in the gold-catalyzed
oxidation reactions and the underlying mechanisms remain under debate. In
this work, we reveal an alternative pathway of O2 activation with the assistance
of H-containing substrates using density functional theory (DFT). It is
demonstrated that the coadsorbed H-containing substrates (R–H) can not only
enhance the adsorption of O2 but also transfer a hydrogen atom to the adjacent
O2, leading to the O2 activation through a hydroperoxyl (OOH) radical species.
The activation barriers of the H-transfer from 16 selected R-H compounds (H2O,
CH3OH, NH2CHCOOH, CH3CH=CH2, (CH3)2SiH2, etc) to the coadsorbed O2 are
lower than 0.50 eV in most cases, indicative of the feasibility of the activation of
O2 via OOH under mild conditions. The formed OOH oxidant, with an
increased O–O bond length of ~1.45 Å , either directly undertakes oxidation
reactions through the end-on oxygen atom or dissociates into atomic oxygen
and hydroxyl (OH) by crossing a fairly low barrier of 0.24 eV. Using CO
oxidation as a probe, we find that OOH has superior activity than activated O2
and atomic oxygen. This study uncovers a new pathway for the activation of O2
and may provide insights for understanding the oxidation catalysis of
nanosized gold.
Accepted: day month year
(automatically inserted by
the publisher)
© Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2015
KEYWORDS
O2 activation, gold cluster,
adsorption, dissociation,
hydroperoxyl
1
Introduction
While bulk gold is chemically inert, the unique
catalytic properties of gold nanoparticles (NPs) have
attracted extensive attention since the pioneering
works by Haruta [1] and Hutchings [2]. In the past
three decades, gold nanoparticles and subnanometer
particles have been successfully applied to a wide
range of reactions, including low-temperature CO
oxidation [3], epoxidation [4, 5], selective
hydrogenation and oxidation [6-8], water-gas shift [9,
10]. Among them, the utilization of gold in oxidation
reactions has aroused particular interest because gold
Address correspondence to Chun-Ran Chang, [email protected]; Jun Li, [email protected]
2
Nano Res.
is capable of catalyzing a variety of oxidation
reactions under extremely mild conditions by use of
molecular oxygen as a feedstock and often with a
high selectivity towards desired products [11].
Despite numerous experimental and theoretical
studies dedicated to the nature of the catalytic
oxidation on gold, the underlying mechanism
remains unclear. Even for the simplest CO oxidation
reaction, the active site and the exact mechanism are
still much debated. A main controversial issue is how
molecular O2 is activated on nanogold catalysts.
Unlike other transition-metal catalysts, molecular
O2 neither adsorbs nor dissociates on bulk gold
surface. Therefore, the activation of O2 is often the
rate-determining step in nanogold catalysis. For
oxide-supported gold catalysts, it is generally
accepted that O2 is activated at the interface between
Au nanoparticles and supports [12-14] or at the
oxygen defects of reducible oxides [15, 16]. The
hydroxyls produced on oxide supports were also
shown to have substantial effects on the activation of
O2 [16, 17]. Another role of oxide supports involves in
modifying the catalytic behavior of Au clusters by
adding [18-22] or removing electrons [9, 23-27].
However, it is difficult to identify which charge or
valance state of Au is mainly responsible for the
catalytic performance. Very recently, Wang et al
presents an interesting picture regarding the charge
transfer in the whole CO oxidation process using ab
initio molecular dynamics (AIMD) simulations[28].
They have demonstrated that the charge state of the
supported Au cluster is dynamically changing
during
the
catalytic
cycle,
where
the
charging/discharging of Au cluster not only controls
the amount of O2 adsorbed at the cluster/oxide
interface but also strongly influences the energetic of
all the redox steps.
To gain an explicit understanding on the
interaction between Au NPs and O2, one simple
approach is to address this issue on bare gold
clusters. It has been shown that small-sized anionic
gold clusters with even-numbered atoms are reactive
with O2, whereas anionic clusters with old-numbered
atoms are inert toward O2 because of lack of
low-lying unpaired electrons [29-31]. The binding
energies of O2 with even-sized Aun– (n = 2, 4, 6)
anions are calculated to be higher than 0.7 eV using
hybrid functional DFT calculations [32]. The
even-odd alternation correlates well to the trend in
the electron affinities of gold clusters [33], suggesting
the electron transfer from anionic cluster to O2 might
be the primary reason for the activation of O2. This
picture was evidenced by anion photoelectron
spectroscopy (PES) and infrared multiple photon
dissociation (IR-MPD) studies [34, 35]. Specifically,
Zeng and coworkers revealed that molecular O2 can
be activated to superoxo- or peroxo-state by small
even-sized Aun– (n = 2 – 18) clusters and the two
states can be converted from one to the other on Au8–,
which further confirms the electron transfer
occurring between anion clusters and adsorbed O2
[36]. Because the high activity of nanogold catalysts
might involve cationic gold [37-39], thus the
interaction between O2 and cationic gold clusters was
also studied in literature. Yoon et al theoretically
reported that positively charged Au clusters can bind
O2 strongly, with a binding energy of 0.46 eV for
Au6O2+, albeit no activation of the O–O bond [40].
Similar conclusion was also drawn by Ding et al
using hybrid functional DFT calculations [32].
Nevertheless, a recent joint experimental and
theoretical work by Woodham et al claim that
cationic gold clusters are capable of activating O2 to
superoxide moieties when multiple oxygen ligands
are complexed with Au clusters [41].
Compared to the charged gold clusters, little is
known about the interaction between neutral gold
clusters and molecular O2 in part due to the lack of
direct experimental detection for uncharged species.
Therefore, theoretical studies are needed to provide
data for assessing such interaction. Hybrid DFT
calculations show that an oscillation behavior also
exists in the interaction between small neutral Au n (n
= 1–6) clusters and O2 [32]. The binding energies of O2
with odd-sized Au3 (0.25 eV) and Au5 (0.64 eV) are
much higher that that with even-sized Au2, 4, 6 clusters
(< 0.1 eV) [32]. This phenomenon was confirmed by
high-level ab initio coupled-cluster (CC) calculations
[42] and IR-MPD spectra [43]. For larger neutral Au
clusters dissociative adsorption of O2 is predicted to
be more favorable than molecular adsorption, but the
dissociation barriers are expected to be ~1 eV or
higher [40, 44]. Barrio et al. employed Au14, Au25, and
Au29 as model systems to show the importance of
unsaturated sites for O2 adsorption [45]. Roldán et al
studied the activation of O2 on a series of neutral
| www.editorialmanager.com/nare/default.asp
3
Nano Res.
gold clusters Aun (n = 5 – 79) and demonstrated that
Au38 is the critical size for O2 adsorption and
dissociation [46, 47].
Although extensive works have been done to study
the interaction between O2 and Au clusters, an
overall understanding on the activation of O2 is still
elusive. Actually, the presence of coadsorbates,
including the reactant molecule itself may have a
substantial effect on the activation of O2. For example,
the dissociation of O2 can be dramatically promoted
by the coadsorbed C2H4, CO, H2O, and atomic
oxygen [48-51]. Our previous studies have also
shown that a coadsorbed water or methanol molecule
not only favors the adsorption of O2 but also transfers
a hydrogen atom to adjacent O2 [52, 53], implying
that the hydrogenation of O2 to OOH might be a new
pathway for the activation of O2. To further elucidate
this OOH pathway for O2 activation, here we carry
out a systematic study on the activation of O2 by
various H-containing substrates, including water,
alcohols, organic acids, amines, and silanes. It is
shown that O2 is capable of abstracting a hydrogen
atom from most of the selected H-containing
substrates with unexpectedly low barriers.
Importantly, in the probe CO oxidation reaction
OOH exhibits superior reactivity than other activated
oxygen species. This study uncovers an alternative
pathway for O2 activation on gold clusters and
nanoparticles.
2
computational model because it has all the necessary
sites and surfaces of a FCC crystal. In addition, size
38 is a “magic” number for cubo-octahedral structure
and is often taken as the representative of large-sized
clusters [59-64]. Au38 (~1 nm) possesses a high
symmetry of Oh and exposes both (111) and (100)
facets and is identified as a critical particle for the
activation of molecular oxygen [46, 47]. During
geometry optimizations, the whole cluster together
with the adsorbate(s) was allowed to relax. The
convergences of energy, gradient, and maximum
displacement were set to 10–5 hartree, 810–4
hartree/Å , and 510–3 Å , respectively. The adsorption
energy Ead of an adsorbate was determined from Ead =
Eads/cluster – (Eads + Ecluster), where Eads/cluster is the total
energy of the Au38 covered with the adsorbate, Eads
the total energy of the adsorbate in the gas phase,
and Ecluster the total energy of the bare Au38 cluster.
The coadsorption energy Ecoad of two adsorbates was
determined from Ecoad = Ecoads/cluster – (Eads1 + Eads2 +
Ecluster), where Ecoads/cluster is the total energy of the Au38
covered with the two adsorbates, Eads1 and Eads2 the
total energy of the first adsorbate and the second
adsorbate in the gas phase, respectively. With these
definitions, a negative value of Ead or Ecoad means a
release of energy or a stable adsorption on the cluster
following the thermodynamic convention.
Computational details
All the calculations were performed using DMol 3
code of the Material Studio package [54, 55]. The
electron exchange and correlation were treated
within generalized-gradient approximation (GGA) in
the form of PBE functional [56]. The localized
double-numerical quality basis set with polarization
functions (DNP) was used. The core electrons of
metal atoms were described using effective core
potentials (ECP) developed by Berger et al [57], in
which the mass-velocity and Darwin relativistic
corrections were introduced. A thermal smearing of
0.002 hartree and a real-space cutoff of 4.5 Å were
applied in our calculations.
A neutral Au38 cluster (Figure 1) with
cubo-octahedral shape, albeit not the global
minimum structure [58], was selected as the
Figure 1
Geometry of Au38 cluster.
The catalytic mechanisms were explored with the
calculations of transition states (TS) and
intermediates, where the TSs were determined by
using complete LST/QST (linear synchronous transit
and quadratic synchronous transit) approach[65] and
a mode-eigenvector following (MEF) method. [66] All
the transition states were confirmed to possess only
one imaginary frequency and the corresponding
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
Research
4
Nano Res.
vibration mode was verified to indeed connect the
reactant and product. The activation barrier Ea is
defined as the energy difference between the TS and
the initial state (IS). The reaction energy ΔE is the
energy difference between the final state (FS) and the
IS. Therefore, a negative value of ΔE means a
thermodynamically favorable process.
3
Results and discussion
3.1 Adsorption and dissociation of O2 on Au38
Before exploring new pathways for O2 activation, we
first discuss the adsorption of O2 on Au38 cluster. As
previously reported [46, 47], molecular O2
preferentially adsorbs at the low-coordinated edge
sites shared by (111) and (100) facets on Au 38.
Therefore, we considered three possible modes for
the adsorption of O2, i.e., η1μ1, η2μ2, η2μ4, which
involve one, two, and four Au–O bond(s),
respectively, as shown in Table 1. For η1μ1, the
Table 1
adsorption energy of O2 is calculated to be –0.32 eV,
suggesting a weak interaction with gold cluster.
However, the O–O bond length, 1.31 Å , is already
elongated by 0.11 Å with respect to that of gas-phase
O2, indicative of a partial activation of adsorbed O2.
As the activation of O2 can be sensitively probed
using spectroscopy, herein we calculated the
vibrational frequencies of adsorbed O2 on Au38.
Experimentally, free O2 has a stretching frequency of
1556 cm-1, while the electron transfer into the π*
orbital of O2 lowers the frequency to 1074 cm-1 for a
superoxo (O2–), or 866 cm-1 for a peroxo (O22–) species
[34]. Therefore, the calculated O–O stretching
frequency (1090 cm-1) in η1μ1 mode together with the
negative charge (–0.25 e) accumulated on adsorbed
O2 suggest that the molecular O2 is activated to a
superoxo-like species. Moreover, the O–O bond
length (1.31 Å ) in η1μ1 mode is close to that in
metal-superoxo complexes in the range of 1.25–1.35
Å [67].
Calculated characteristics of O2 adsorption on Au38 cluster
Adsorption
Optimized
Ead(O2)
d(Au–O)
d(O–O)
ν(O–O) a
q(O2) b
mode
geometry
/eV
/Å
/Å
/cm-1
/e
η1μ1
–0.32
2.23
1.31
1090
–0.25
η2μ2
–0.56
1.34
971
–0.36
1.42
733
–0.50
2.16
2.17
2.34
η2μ4
–0.61
2.34
2.35
2.35
a
Stretching frequency of adsorbed O2. b Mulliken charge of adsorbed O2.
Compared to η1μ1 mode, the adsorption of O2 in
η2μ2 mode is slightly improved in light of the
increased adsorption energy (–0.56 eV), the longer
O–O bond (1.34 Å ), the more negative q(O2) (–0.36 e),
and the decreased O–O stretching frequency (971
cm-1). These features are still close to those of
superoxo, thus the activated O2 in η2μ2 mode can also
be classified as a superoxo-like species. While for the
| www.editorialmanager.com/nare/default.asp
5
Nano Res.
η2μ4 mode, the adsorption of O2 is further enhanced
with an adsorption energy of –0.61 eV. Each oxygen
atom of O2 is bridged over two Au atoms. In
particular, the O–O bond is notably elongated by 0.21
Å with respect to that of free O2, close to the typical
value (1.40–1.50 Å ) of metal-peroxo complexes [67].
Therefore, from η1μ1 to η2μ4 the adsorbed O2
experienced a transition from superoxo- to
peroxo-adsorption, similar to the episode on anion
Au8– cluster [36]. The η2μ2 adsorption can be regarded
as an intermediate for this transition.
From the abovementioned results, it is clear that
molecular O2 can be partially activated through
chemisorption on gold clusters when it becomes
feasible to transfer electron(s) to triplet O2. In
appearance, the degree of the O2 activation is
strongly dependent on the adsorption modes, but
actually the amount of electrons transferred from
gold cluster to O2 is the underlying determining
factor. As shown in Table 1, the more electrons
accumulated on adsorbed O2, the longer O–O bond
length and the lower O–O stretching frequency will
be, indicative of the better activation of O2. Moreover,
as the negative charge on O2 increases, the
adsorption of O2 on gold cluster becomes more stable.
These results well support the viewpoint that the
electronic structure is the link between the physical
structure of a material and the functionality [68].
Although O2 can be partially activated via
adsorption, the dissociation of O2 into atomic oxygen
is usually considered as the complete pathway for O2
activation. Figure 2 depicts the energy profile for the
dissociation of O2 on Au38 upon the η2μ2 and η2μ4
modes. We find that the direct dissociation of O2
from η2μ2 mode needs to overcome a high barrier of
2.06 eV, although the thermodynamics is favored by
0.66 eV. However, the dissociation of O2 from η2μ4
mode is more feasible with an activation barrier of
0.64 eV and an energy release of –0.62 eV, comparable
with previous study [46, 47]. The large deviation
between the two barriers can be ascribed to the
varied structure of the transition states. In TS1, two
nearly separated O atoms adsorb at the top sites of
Au, which is extremely unstable due to the electron
unsaturation. While in TS2, each O atom locates at a
bridge site of two Au atoms, where the O–O bond
cleavage can be effectively compensated by Au–O
interactions. For the two pathways, the dissociated
oxygen atoms all bind strongly at the three-fold
hollow sites of gold, which explains why the
dissociative adsorption of O2 is energetically
favorable on some larger gold clusters [40].
Figure 2 Energy profiles for the dissociation of O2 on Au38.
The zero energy level refers to the total energy of bare Au 38 and
gas-phase O2.
3.2 Hydrogenation of O2 to OOH on Au38
While the dissociation of O2 is feasible on Au38 cluster,
it becomes more difficult on larger or smaller gold
clusters due to the high barriers [40, 47]. Therefore, in
this section we discuss a new pathway for the
activation of O2 by hydrogen-abstraction from
H-containing substrates (R–H) that avoids direct O2
dissociation. The R–H substrates are selected from
the most commonly used solvents or reactants that
may involve in oxidation reactions, including water,
alcohols, amines, amino acids, and hydrocarbons.
Table 2 lists the activation barriers (Ea) and reaction
energies (ΔE) for O2 reacting with 16 selected R–H
substrates. Figure 3 displays the optimized structures
of the initial states (IS), transition states (TS) and final
states (FS) of the 16 reactions.
For a catalytic reaction involving two or more
reactants, trapping the reactants within a suitable
region is always a necessary step. After searching for
several possible adsorption sites, we find that O2 and
R–H prefer to coadsorbed on the low-coordinated
(100) facet of Au38, as shown in the IS structures of
Figure 3. Importantly, the two neighboring Au atoms
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
Research
6
Nano Res.
on (100) facet distanced by ~3 Å are capable of
trapping O2 and R-H within a reactive region. Our
calculation results reveal that the coadsorption of O2
and R–H exhibits a cooperative effect in most cases.
For example, the coadsorption energy of O2 and H2O
is calculated to be –0.98 eV, which is 0.40 eV (in
absolute value) higher than the sum of the separated
adsorption energy of H2O and O2, indicating that the
coadsorption is cooperative but not competitive. The
Table 2
coadsorption energy of O2 and C6H5NH2, –1.25 eV, is
0.31 eV (in absolute value) higher than that of
separated adsorptions. Such cooperative effect in
coadsorption is ascribed to the hydrogen bonding
interaction between R–H and O2, which is more
notable for substrates involving O–H and N–H bonds
than the ones involving C–H and Si–H bonds, as
revealed by the calculation results in Table 2.
Calculated coadsorption energies (Ecoad) of H-containing substrates (R-H) and O2, the activation barriers (Ea), and reaction
energies (ΔE) of O2* + R-H* → *OOH + R* on Au38
R-H
Reactions
a
Ecoad / eV
Ea / eV
ΔE / eV
–0.98
0.26
0.19
–1.03
0.29
0.23
–0.95
0.21
–0.01
H-abstraction from O-H bond
1
water
2
methanol
3
phenol
4
5
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
O2 + CH3OH → OOH + CH3O
*
O2 + C6H5OH → OOH + C6H5O
O2 + HCOOH → OOH + HCOO
–0.79
0.25
–0.13
*
–0.87
0.22
–0.11
O2 + NH2CHCOOH → OOH + NHCHCOOH
–1.19
0.22
0.21
–1.25
0.32
0.25
formic acid
glycine
*
O2 + H2O → OOH + OH
*
O2 + NH2CHCOOH → OOH + NH2CHCOO
H-abstraction from N-H bond
6
glycine
7
phenylamine
*
*
*
*
*
*
*
*
O2 + C6H5NH2 → OOH + C6H5NH
H-abstraction from C-H bond
8
*
*
*
*
–0.43
1.03
–0.24
*
*
*
*
–0.85
0.68
–0.04
*
*
*
*
–0.87
0.19
–0.54
*
*
–0.52
0.20
0.07
*
*
–0.54
0.29
0.20
*
*
*
*
–0.80
0.28
0.11
*
*
*
*
–0.52
0.42
0.02
–0.39
0.31
–1.21
–0.51
0.06
–1.40
O2 + CH4 → OOH + CH3
methane
9
ethylene
O2 + C2H4 → OOH + C2H3
10
acetylene
O2 + C2H2 → OOH + C2H
11
acetaldehyde
12
acetone
13
propylene
14
ethylbenzene
*
*
O2 + CH3CHO → OOH + CH2CHO
*
*
O2 + CH3COCH3 → OOH + CH2COCH3
O2 + CH3CH=CH2 → OOH + CH2CH=CH2
O2 + C6H5CH2CH3 → OOH + C6H5CHCH3
H-abstraction from Si-H bond
15
16
a
*
dimethylsilane
*
*
*
*
*
O2 + SiH4 → OOH + SiH3
silane
*
O2 + (CH3)2SiH2 → OOH + (CH3)2SiH
*
An asterisk (*) represents the adsorbed state.
In the coadsorbed structures, O2 is only slightly
activated in light of the O–O bond length being
around 1.30 Å , thus further activation is needed.
Subsequently, the reactions between R–H and O2 are
investigated thermodynamically and kinetically.
Depending on the origin of the H atoms, these
reactions are classified into four groups, i.e.,
H-abstraction from O–H bond, N–H bond, C–H bond,
| www.editorialmanager.com/nare/default.asp
7
Nano Res.
and Si–H bond. In the first group, water is selected as
a special H-containing substance for study due to its
existence in a variety of chemical systems, either as
moisture or solvent or reactant, or oxidation product.
In particular, water was shown to have a promotional
effect in a number of chemical reactions [69-77].
Calculation results show that O2 can readily abstract
a hydrogen atom from coadsorbed H2O to form OOH,
with a low barrier of 0.26 eV and a reaction energy of
0.19 eV. Although this step alone is slightly
endothermic, the energy cost can be compensated in
other elementary steps or at temperatures higher
than zero Kelvin. A recent joint experimental and
theoretical work by Saavedra et al. confirms the
generation of OOH on Au/TiO2 catalyst in the
presence of water [78], which is consistent with our
previous OOH mechanism.48 The hydrogen transfer
from methanol to O2 is analogous to that of H2O, the
activation barrier and reaction energy of which are
calculated to be 0.29 eV and 0.23 eV, respectively. In
comparison of the above results with those on bulk
Au(111) surface [53], the hydrogenation of O2 to
OOH by H2O or CH3OH is much easier on Au38,
which is mainly attributed to the fact that the
low-coordination sites on Au38 can benefit the
coadsorption of O2 and H2O (or CH3OH) as well as
the H-transfer processes. While compared with our
previous results on Au10 subnanometer cluster [52] ,
the hydrogen transfer from H2O to O2 on Au38 is
slightly more difficult, as is expected. In this group of
selected species, we also investigated the
H-abstraction reactions from phenol, formic acid, and
glycine, which are shown to be more favorable in
thermodynamics and kinetics than the cases of H2O
and CH3OH. The exothermicity of these reactions
suggests that the activation of O2 via OOH is more
favorable in an acidic environment. Of particular
interest is the reaction between O2 and glycine since
O2 can abstract a hydrogen atom either from
carboxyl- or amino-group. The former turns out to be
a little easier than the latter according to the reaction
energies listed in Table 2. The H-abstraction from
–COOH or –NH2 can also be expected in other amino
acids, which may provide novel insights into the
activation of O2 in biosystems under certain
conditions. One more example for the H-abstraction
from N–H bond is the reaction between O2 and
phenylamine, the activation barrier and reaction
energy is calculated to be 0.32 eV and 0.25 eV,
respectively.
Based on these results, we discuss hydrogen
abstraction by O2 from C–H and Si–H bonds. Since
alkanes are inert as the noble gases in organic
chemistry [79], it is not surprising that the H-transfer
from CH4 to O2 has a quite high barrier of 1.03 eV. In
fact, CH4 only weakly physisorbs on Au38 via a
hydrogen atom, reflecting the difficulty in activating
C–H σ-bond. Compared to CH4, the H-abstraction
from C2H4 and C2H2 are relatively easier, with
activation barriers of 0.68 eV and 0.19 eV, respectively.
Because α-H usually presents high activity in
chemical reactions, we hence further inspect the
reaction between O2 and the α-H contained in
acetaldehyde, acetone, propylene, and ethylbenzene.
Calculation results show that the α-H-abstraction by
O2 is facile to take place with activation barriers
falling between 0.20 eV and 0.42 eV. These results
indicate that the α-H might serve as an initiator for
the activation of O2 in some systems. Although the
other types of hydrogen atoms, such as β-H, may also
contribute to O2 activation, the activity is much lower
than that of α-H, thus they are not considered in the
current work. Finally, the H-abstraction from silane
and dimethylsilane are also calculated, which have
activation barriers of 0.31 and 0.06 eV, and reaction
energies of –1.21 eV and –1.40 eV, respectively.
From the results above, one can see that the
barriers for the activation of O2 to OOH by the 16
selected R-H substrates are lower than 0.50 eV with
the exceptions of methane and ethylene. Although
the DFT calculations with GGA exchange-correlation
functional might have underestimated the barriers,
the comparison with the O2 dissociation pathway
does suggest that the OOH-activation pathway is
more favorable. After hydrogenation, the O–O bond
length of OOH has been elongated to 1.45 Å , nearly
20% longer than that of free O2, indicating that
molecular O2 is substantially activated. The formed
OOH can either serve as an oxidant or dissociate into
two oxidizing agents of O and OH for further
oxidation, which will be discussed in the next section.
Theoretically, the activation of O2 by an extra ligand
has been demonstrated previously in the interaction
between O2 and Xe+ via a (p-π*)σ bonding [80].
Similarly, the activation of O2 by an extra H atom can
be explained by the formation of a (s-π*)σ bonding,
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
Research
8
Nano Res.
which leads to the π* anti-bonding MOs of O2 being
partially occupied and thus the O–O bond being
weakened. Experimentally, the OOH species is
observed by in situ UV/Vis in the presence of O2 and
Figure 3
H2O [70]. These results provide strong support for
the activation of O2 along the alternative
OOH-pathway.
Optimized geometries of the initial states (IS), transition states (TS), and final states (FS) of reactions 1-16 listed in Table 2.
| www.editorialmanager.com/nare/default.asp
9
Nano Res.
3.3
CO oxidation by activated oxygen species
To further study how OOH involves in oxidation
reactions, we select CO oxidation reaction as a probe
for the mechanistic study. Figure 4 (from left to right)
displays the energy profiles for the oxidation of CO
to CO2 with activated O2, atomic O, and OOH,
respectively. For CO oxidation by activated O2
molecule, CO and O2 favorably coadsorb on two
neighboring Au atoms of Au38 cluster with a
coadsorption energy of –0.94 eV. Through the
coadsorption structure, CO and O2 can move closer
to each other and arrive at an O–O–C–O intermediate,
accompanied with an energy release of 0.80 eV. The
structure of this intermediate is analogous to that on
small-sized gold clusters, as reported previously
[81-83]. The O–O bond length of O–O–C–O is
Figure 4
measured at 1.45 Å , much longer than the value, 1.31
Å , of solely-adsorbed O2. After crossing a barrier of
0.64 eV, a CO2 molecule is formed and subsequently
desorbs into gas-phase exothermically by 2.35 eV.
While for the CO oxidation with atomic O, a suitable
site for the coadsorption of the two species cannot be
located because once CO and O approach, a CO2
molecule will be generated immediately. Therefore,
the reaction between CO and atomic O might follow
an Eley-Rideal mechanism on Au38, with atomic O
adsorbed on gold cluster and CO in the gas phase. As
shown in the middle column of Figure 4, the
activation barrier and reaction energy are calculated
to be 0.47 eV and –2.62 eV, respectively, suggesting
that atomic oxygen is more active than activated O2
in the oxidation of CO.
Energy profiles for the CO oxidation with activated O2, atomic oxygen, and OOH.
The CO oxidation reaction via OOH is very similar
to that by activated O2. CO and OOH also coadsorb
on two neighboring low-coordinated Au atoms of
Au38 with CO adjacent to the end-on oxygen atom of
OOH. In the presence of coadsorbed CO, the O–O
bond of OOH is elongated to 1.47 Å , even longer
than the original O–O distance in OOH (1.45 Å ).
Through this coadsorption structure, a CO2 molecule
can be readily produced via combination of CO with
the end-on oxygen of OOH, leaving a hydroxyl being
adsorbed on Au38. The activation barrier and reaction
energy are calculated to be 0.31 eV and –3.99 eV,
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
Research
10
Nano Res.
respectively. In comparison of the three energy
profiles in Figure 4, we find that the CO oxidation by
OOH is the most favorable to occur. The
extraordinary behavior of OOH is attributed to the
much weakened O–O bond in OOH, which causes
the end-on oxygen atom of OOH being more easily
abstracted than that of activated O2 and atomic
oxygen. As an alternative to the OOH serving as an
oxidative species, OOH can also dissociate into O
and OH by overcoming a relatively low barrier of
0.24 eV, as depicted in Figure 5. Although the
hydroxyl is also found to play an important role in
oxidation catalysis by gold nanoparticles [84], we will
not explore this aspect in the current work because
oxidation reactions via hydroxyl were discussed in
our previous work [52, 53].
alternative to the O2 dissociation, the hydrogenation
of O2 to OOH by hydrogen-abstraction from
H-containing substrates (R–H) is found to be a more
preferred pathway for facile activation of O2. The
activation barriers of H-transfer from R–H to O2 are
less than 0.50 eV for most of the selected R-H
substrates, implying the activation of O2 via OOH is
feasible on gold nanoparticles at room temperature.
After hydrogenation, the O–O distance of OOH is
increased by ~20% with respect to that of gas-phase
O2, indicative of the strong activation of O–O bond.
The formed OOH can either directly perform
oxidation reactions or dissociate into strong oxidants
of atomic oxygen and hydroxyl. Among the CO
oxidation reactions via activated O2, atomic oxygen
and OOH, the OOH radical exhibits extraordinary
activity compared to the other two oxidative species,
with an activation barrier of 0.31 eV and a huge
energy release of 3.99 eV. This study thus illustrates
an alternative pathway for the activation of
molecular O2 and may provide insights for
understanding the complicated mechanisms of
catalytic oxidation on gold catalysts.
Acknowledgements
Figure 5 Energy profile for the dissociation of OOH into
atomic oxygen and hydroxyl.
4
Conclusions
This work was supported by the National Key Basic
Research Special Foundations (2011CB932400), the
China
Postdoctoral
Science
Foundation
(2014M562391), and the Fundamental Research
Funds for the Central Universities (xjj2014064). The
calculations
were
performed
by
using
supercomputers at the Computer Network
Information Center, Chinese Academy of Sciences,
Tsinghua National Laboratory for Information
Science and Technology, and the Shanghai
Supercomputing Center.
References
We have performed a systematic computational
study of the activation of molecular O2 on a selected
Au38 cluster using density functional theory. It is
found that molecular O2 can be primarily activated
via superoxo/peroxo-like adsorption on Au38. The
amount of electrons transferred from gold cluster to
the π* orbital of O2 is recognized as the underlying
determining factor for the activation of O2. As an
[1]
Haruta, M.;Kobayashi, T.;Sano, H.; Yamada, N. Novel
gold catalysts for the oxidation of carbon monoxide at a
temperature far below 0 °C. Chem. Lett. 1987, 16,
405-408.
[2]
Hutchings, G. J. Vapor-phase hydrochlorination of
acetylene: correlation of catalytic activity of supported
metal chloride catalysts. J. Catal. 1985, 96, 292-295.
| www.editorialmanager.com/nare/default.asp
11
Nano Res.
[3]
[4]
Haruta, M. Size- and support-dependency in the catalysis
of gold. Catal. Today 1997, 36, 153-166.
on the Localized Electronic States and Their Potential
Nijhuis, T. A.;Visser, T.; Weckhuysen, B. M. Mechanistic
Role During H2O Dissociation and CO Oxidation
study into the direct epoxidation of propene over
Processes on CeO2(111) Surface. J. Phys. Chem. C 2013,
gold/titania catalysts. J. Phys. Chem. B 2005, 109,
117, 23082-23089.
19309-19319.
[5]
[6]
[7]
[8]
[9]
[16] Wang, Y.-G.;Mei, D.;Li, J.; Rousseau, R. DFT+U Study
[17] Liu, L. M.;McAllister, B.;Ye, H. Q.; Hu, P. Identifying an
Sinha, A. K.;Seelan, S.;Tsubota, S.; Haruta, M. Catalysis
O2 supply pathway in CO oxidation on Au/TiO2(110): a
by gold nanoparticles: epoxidation of propene. Top. Catal.
density functional theory study on the intrinsic role of
2004, 29, 95-102.
water. J. Am. Chem. Soc. 2006, 128, 4017-4022.
McEwan, L.;Julius, M.;Roberts, S.; Fletcher, J. C. Q. A
[18] Chen, M.;Cai, Y.;Yan, Z.; Goodman, D. W. On the origin
review of the use of gold catalysts in selective
of the unique properties of supported Au nanoparticles. J.
hydrogenation reactions. Gold Bull. 2010, 43, 298-306.
Am. Chem. Soc. 2006, 128, 6341-6346.
Corma, A.; Serna, P. Chemoselective hydrogenation of
[19] Remediakis, I. N.;Lopez, N.; Nørskov, J. K. CO oxidation
nitro compounds with supported gold catalysts. Science
on rutile-supported Au nanoparticles. Angew. Chem. Int.
2006, 313, 332-334.
Ed. 2005, 44, 1824-1826.
Della Pina, C.;Falletta, E.;Prati, L.; Rossi, M. Selective
[20] Wörz, A. S.;Heiz, U.;Cinquini, F.; Pacchioni, G. Charging
oxidation using gold. Chem. Soc. Rev. 2008, 37,
of Au atoms on TiO2 thin films from CO vibrational
2077-2095.
spectroscopy and DFT calculations. J. Phys. Chem. B
Fu, Q.;Saltsburg, H.; Flytzani-Stephanopoulos, M. Active
nonmetallic Au and Pt species on ceria-based water-gas
[21] Madsen, G. K. H.; Hammer, B. Effect of subsurface
Ti-interstitials on the bonding of small gold clusters on
shift catalysts. Science 2003, 301, 935-938.
[10] Bond, G. Mechanisms of the gold-catalysed water-gas
rutile TiO2(110). J. Chem. Phys. 2009, 130, 044704.
[22] Yoon,
shift. Gold Bull. 2009, 42, 337-342.
[11] Hashmi, A. S. K.; Hutchings, G. J. Gold catalysis. Angew.
B.;Häkkinen,
H.;Landman,
U.;Wörz,
A.
S.;Antonietti, J. M.;Abbet, S.;Judai, K.; Heiz, U.
Charging effects on bonding and catalyzed oxidation of
Chem. Int. Ed. 2006, 45, 7896-7936.
[12] Green, I. X.;Tang, W.;Neurock, M.; Yates Jr., J. T.
Spectroscopic observation of dual catalytic sites during
oxidation of CO on a Au/TiO2 catalyst. Science 2011, 333,
CO on Au8 clusters on MgO. Science 2005, 307, 403-407.
[23] Fu, L.;Wu, N. Q.;Yang, J. H.;Qu, F.;Johnson, D. L.;Kung,
M. C.;Kung, H. H.; Dravid, V. P. Direct evidence of
oxidized gold on supported gold catalysts. J. Phys. Chem.
736-739.
[13] Widmann, D.; Behm, R. J. Activation of molecular
oxygen and the nature of the active oxygen species for
CO oxidation on oxide supported Au catalysts. Acc.
B 2005, 109, 3704-3706.
[24] Bond, G. C.; Thompson, D. T. Gold-catalysed oxidation
of carbon monoxide. Gold Bull. 2000, 33, 41-51.
[25] Wang, J. G.; Hammer, B. Role of Au+ in supporting and
Chem. Res. 2014, 47, 740-749.
[14] Green, I. X.;Tang, W.;Neurock, M.; Yates, J. T. Insights
into catalytic oxidation at the Au/TiO2 dual perimeter
activating Au7 on TiO2(110). Phys. Rev. Lett. 2006, 97,
136107.
[26] Liu, Z. P.;Jenkins, S. J.; King, D. A. Origin and activity of
sites. Acc. Chem. Res. 2013, 47, 805-815.
[15] Wang, Y.-G.;Mei, D.;Glezakou, V.-A.;Li, J.; Rousseau, R.
Dynamic formation of single-atom catalytic active sites
on ceria-supported gold nanoparticles. Nat Commun 2015,
6, 6511.
2005, 109, 18418-18426.
oxidized gold in water-gas-shift catalysis. Phys. Rev. Lett.
2005, 94, 196102.
[27] Zhang, C.;Michaelides, A.;King, D. A.; Jenkins, S. J.
Positive charge states and possible polymorphism of gold
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
Research
12
Nano Res.
nanoclusters on reduced ceria. J. Am. Chem. Soc. 2010,
C.;Guzman, J.; Gates, B. C. Role of gold cations in the
132, 2175-2182.
oxidation of carbon monoxide catalyzed by iron
[28] Wang, Y.-G.;Yoon, Y.;Glezakou, V.-A.;Li, J.; Rousseau, R.
oxide-supported gold. J. Catal. 2006, 242, 71-81.
The role of reducible oxide–metal cluster charge transfer
[38] Guzman, J.; Gates, B. C. Oxidation states of gold in
in catalytic processes: new insights on the catalytic
MgO-supported complexes and clusters: characterization
mechanism of CO oxidation on Au/TiO2 from ab initio
by
molecular dynamics. J. Am. Chem. Soc. 2013, 135,
temperature-programmed oxidation and reduction. J.
10673-10683.
Phys. Chem. B 2003, 107, 2242-2248.
X-ray
absorption
spectroscopy
and
[29] Cox, D. M.;Brickman, R.;Creegan, K.; Kaldor, A. Gold
[39] Guzman, J.; Gates, B. C. Catalysis by supported gold:
clusters: reactions and deuterium uptake. Z. Phys.
correlation between catalytic activity for CO oxidation
D-Atoms Molecules and Clusters 1991, 19, 353-355.
and oxidation states of gold. J. Am. Chem. Soc. 2004, 126,
[30] Lee, T. H.; Ervin, K. M. Reactions of copper group
cluster anions with oxygen and carbon-monoxide. J. Phys.
2672-2673.
[40] Yoon, B.;Häkkinen, H.; Landman, U. Interaction of O2
with gold clusters: molecular and dissociative adsorption.
Chem. 1994, 98, 10023-10031.
[31] Salisbury, B. E.;Wallace, W. T.; Whetten, R. L.
J. Phys. Chem. A 2003, 107, 4066-4071.
Low-temperature activation of molecular oxygen by gold
[41] Woodham, A. P.; Fielicke, A. Superoxide formation on
clusters: a stoichiometric process correlated to electron
isolated cationic gold clusters. Angew. Chem. Int. Ed.
affinity. Chem. Phys. 2000, 262, 131-141.
2014, 53, 6554-6557.
[32] Ding, X. L.;Li, Z. Y.;Yang, J. L.;Hou, J. G.; Zhu, Q. S.
[42] Zhao, Y.;Khetrapal, N. S.;Li, H.;Gao, Y.; Zeng, X. C.
Adsorption energies of molecular oxygen on Au clusters.
Interaction between O2 and neutral/charged Au n (n=1-3)
J. Chem. Phys. 2004, 120, 9594-9600.
clusters: A comparative study between density-functional
[33] Taylor, K. J.;Pettiettehall, C. L.;Cheshnovsky, O.;
Smalley, R. E. Ultraviolet photoelectron-spectra of
coinage metal-clusters. J. Chem. Phys. 1992, 96,
3319-3329.
theory and coupled cluster calculations. Chem. Phys. Lett.
2014, 592, 127-131.
[43] Woodham, A. P.;Meijer, G.; Fielicke, A. Charge
Separation Promoted Activation of Molecular Oxygen by
[34] Woodham, A. P.;Meijer, G.; Fielicke, A. Activation of
molecular oxygen by anionic gold clusters. Angew. Chem.
Neutral Gold Clusters. J. Am. Chem. Soc. 2013, 135,
1727-1730.
[44] Wang, Y.; Gong, X. G. First-principles study of
Int. Ed. 2012, 51, 4444-4447.
[35] Huang, W.;Zhai, H.-J.; Wang, L.-S. Probing the
interactions of O2 with small gold cluster anions (Aun−, n
= 1−7): chemisorption vs physisorption. J. Am. Chem.
interaction of cluster Au32 with CO, H2, and O2. J. Chem.
Phys. 2006, 125, 124703.
[45] Barrio, L.;Liu, P.;Rodriguez, J. A.;Campos-Martin, J. M.;
Fierro, J. L. G. Effects of hydrogen on the reactivity of O2
Soc. 2010, 132, 4344-4351.
[36] Pal, R.;Wang, L.-M.;Pei, Y.;Wang, L.-S.; Zeng, X. C.
Unraveling the mechanisms of O2 activation by
size-selected gold clusters: transition from superoxo to
toward gold nanoparticles and surfaces. J. Phys. Chem. C
2007, 111, 19001-19008.
[46] Roldán, A.;González, S.;Ricart, J. M.; Illas, F. Critical
peroxo chemisorption. J. Am. Chem. Soc. 2012, 134,
size
for
O2
dissociation
by
9438-9445.
ChemPhysChem 2009, 10, 348-351.
Au
nanoparticles.
[37] Hutchings, G. J.;Hall, M. S.;Carley, A. F.;Landon,
[47] Roldán, A.;Ricart, J. M.;Illas, F.; Pacchioni, G. O2
P.;Solsona, B. E.;Kiely, C. J.;Herzing, A.;Makkee,
adsorption and dissociation on neutral, positively and
M.;Moulijn, J. A.;Overweg, A.;Fierro-Gonzalez, J.
negatively charged Aun (n = 5-79) clusters. Phys. Chem.
| www.editorialmanager.com/nare/default.asp
13
Nano Res.
nano-clusters in the presence of CO: a combined DFT
Chem. Phys. 2010, 12, 10723-10729.
[48] Lyalin, A.; Taketsugu, T. Reactant-promoted oxygen
dissociation on gold clusters. J. Phys. Chem. Lett. 2010, 1,
1752-1757.
and DRIFTS study. J. Catal. 2013, 308, 272-281.
[60] Paz-Borbón, L. O.;Johnston, R. L.;Barcaro, G.; Fortunelli,
A. Structural motifs, mixing, and segregation effects in
[49] Gao, Y.; Zeng, X. C. Water-promoted O2 dissociation on
small-sized anionic gold clusters. ACS Catal. 2012, 2,
2614-2621.
38-atom binary clusters. J. Chem. Phys. 2008, 128,
134517.
[61] Pittaway, F.;Paz-Borbón, L. O.;Johnston, R. L.;Arslan,
[50] Liu, C.;Tan, Y.;Lin, S.;Li, H.;Wu, X.;Li, L.;Pei, Y.; Zeng,
H.;Ferrando, R.;Mottet, C.;Barcaro, G.; Fortunelli, A.
X. C. CO self-promoting oxidation on nanosized gold
Theoretical studies of palladium-gold nanoclusters:
clusters: triangular Au3 active site and CO induced O–O
Pd-Au clusters with up to 50 Atoms. J. Phys. Chem. C
scission. J. Am. Chem. Soc. 2013, 135, 2583-2595.
2009, 113, 9141-9152.
[51] Deng, X. Y.;Min, B. K.;Guloy, A.; Friend, C. M.
[62] Ismail, R.; Johnston, R. L. Investigation of the structures
Enhancement of O2 dissociation on Au(111) by adsorbed
and chemical ordering of small Pd-Au clusters as a
oxygen: implications for oxidation catalysis. J. Am. Chem.
function of composition and potential parameterisation.
Soc. 2005, 127, 9267-9270.
Phys. Chem. Chem. Phys. 2010, 12, 8607-8619.
Theoretical
[63] West, P. S.;Johnston, R. L.;Barcaro, G.; Fortunelli, A. The
investigations of the catalytic role of water in propene
effect of CO and H chemisorption on the chemical
epoxidation
ordering of bimetallic clusters. J. Phys. Chem. C 2010,
[52] Chang,
C.-R.;Wang,
on
Y.-G.;
Li,
gold
J.
nanoclusters:
a
hydroperoxyl-mediated pathway. Nano Res. 2011, 4,
131-142.
114, 19678-19686.
[64] Roldán, A.;Manel Ricart, J.; Illas, F. Influence of the
A
exchange-correlation potential on the description of the
water-promoted mechanism of alcohol oxidation on a
molecular mechanism of oxygen dissociation by Au
Au(111) surface: understanding the catalytic behavior of
nanoparticles. Theor. Chem. Acc. 2009, 123, 119-126.
[53] Chang,
C.-R.;Yang,
X.-F.;Long,
B.;
Li,
J.
[65] Baker, J. An algorithm for the location of transition-states.
bulk gold. ACS Catal. 2013, 3, 1693-1699.
[54] Delley, B. An all-electron numerical method for solving
the local density functional for polyatomic molecules. J.
[55] Delley, B. From molecules to solids with the
Dmol3
[56] Perdew, J. P.;Burke, K.; Ernzerhof, M. Generalized
gradient approximation made simple. Phys. Rev. Lett.
[67] Sahoo, B.;Nayak, C. N.;Samantaray, A.; Kumar, P.
Inorganic Chemsitry; PHI Learning: New Delhi, 2012.
[68] Nørskov, J. K.;Bligaard, T.;Rossmeisl, J.; Christensen, C.
1996, 77, 3865-3868.
[57] Bergner, A.;Dolg, M.;Küchle, W.;Stoll, H.; Preuß, H. Ab
initio energy-adjusted pseudopotentials for elements of
[58] Jiang, D.-e.; Walter, M. Au40: A large tetrahedral magic
Nat. Chem. 2009, 1, 37-46.
over Au/TiO2 catalyst. J. Catal. 2001, 201, 221-224.
[70] Huang, J.;Akita, T.;Faye, J.;Fujitani, T.;Takei, T.; Haruta,
cluster. Phys. Rev. B 2011, 84, 193402.
[59] Zhu, B.;Thrimurthulu, G.;Delannoy, L.;Louis, C.;Mottet,
C.;Creuze, J.;Legrand, B.; Guesmi, H. Evidence of Pd
at
H. Towards the computational design of solid catalysts.
[69] Daté, M.; Haruta, M. Moisture effect on CO oxidation
groups 13-17. Mol. Phys. 1993, 80, 1431-1441.
stabilization
for transition state location. Comput. Mater. Sci. 2003, 28,
250-258.
approach. J. Chem. Phys. 2000, 113, 7756-7764.
and
[66] Govind, N.;Petersen, M.;Fitzgerald, G.;King-Smith, D.;
Andzelm, J. A generalized synchronous transit method
Chem. Phys. 1990, 92, 508-517.
segregation
J. Comput. Chem. 1986, 7, 385-395.
edges
of
AuPd
M. Propene epoxidation with dioxygen catalyzed by gold
clusters. Angew. Chem. Int. Ed. 2009, 48, 7862-7866.
[71] Lee,
S.;Molina,
L.
M.;López,
M.
J.;Alonso,
www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano
J.
Research
14
Nano Res.
A.;Hammer, B.;Lee, B.;Seifert, S.;Winans, R. E.;Elam, J.
[81] Lopez, N.; Nørskov, J. K. Catalytic CO oxidation by a
W.;Pellin, M. J.; Vajda, S. Selective propene epoxidation
gold nanoparticle: A density functional study. J. Am.
on immobilized Au6-10 clusters: the effect of hydrogen
Chem. Soc. 2002, 124, 11262-11263.
and water on activity and selectivity. Angew. Chem. Int.
Ed. 2009, 48, 1467-1471.
[82] Sanchez,
A.;Abbet,
S.;Heiz,
U.;Schneider,
W.
D.;Häkkinen, H.;Barnett, R. N.; Landman, U. When gold
[72] Ojeda, M.; Iglesia, E. Catalytic epoxidation of propene
with H2O-O2 reactants on Au/TiO2. Chem. Commun.
2009, 352-354.
is not noble: nanoscale gold catalysts. J. Phys. Chem. A
1999, 103, 9573-9578.
[83] Liu, Z. P.;Gong, X. Q.;Kohanoff, J.;Sanchez, C.; Hu, P.
[73] Vöhringer-Martinez,
E.;Hansmann,
B.;Hernandez,
Catalytic role of metal oxides in gold-based catalysts: A
H.;Francisco, J. S.;Troe, J.; Abel, B. Water catalysis of a
first principles study of CO oxidation on TiO2 supported
radical-molecule gas-phase reaction. Science 2007, 315,
Au. Phys. Rev. Lett. 2003, 91, 266102.
497-501.
[84] Ide, M. S.; Davis, R. J. The important role of hydroxyl on
[74] Long, B.;Tan, X.-F.;Ren, D.-S.; Zhang, W.-J. Theoretical
studies
on
energetics
and
mechanisms
of
the
oxidation catalysis by gold nanoparticles. Acc. Chem. Res.
2013, 47, 825-833.
decomposition of CF3OH. Chem. Phys. Lett. 2010, 492,
214-219.
[75] Long, B.;Zhang, W.-J.;Tan, X.-F.;Long, Z.-W.;Wang,
Y.-B.; Ren, D.-S. Theoretical study on the gas phase
reaction of sulfuric acid with hydroxyl radical in the
presence of water. J. Phys. Chem. A 2011, 115,
1350-1357.
[76] Long, B.;Chang, C. R.;Long, Z. W.;Wang, Y. B.;Tan, X.
F.; Zhang, W. J. Nitric acid catalyzed hydrolysis of SO3 in
the formation of sulfuric acid: a theoretical study. Chem.
Phys. Lett. 2013, 581, 26-29.
[77] Long, B.;Tan, X.-F.;Chang, C.-R.;Zhao, W.-X.;Long,
Z.-W.;Ren, D.-S.; Zhang, W.-J. Theoretical Studies on
Gas-Phase
Reactions
of Sulfuric
Acid
Catalyzed
Hydrolysis of Formaldehyde and Formaldehyde with
Sulfuric Acid and H2SO4···H2O Complex. J. Phys.
Chem. A 2013, 117, 5106-5116.
[78] Saavedra, J.;Doan, H. A.;Pursell, C. J.;Grabow, L. C.;
Chandler, B. D. The Critical Role of Water at the
Gold-Titania Interface in Catalytic CO Oxidation.
Science 2014, 345, 1599-1602.
[79] Shilov, A. E.; Shul'pin, G. B. Activation of C-H bonds by
metal complexes. Chem. Rev. 1997, 97, 2879-2932.
[80] Zhou, M.;Zhao, Y.;Gong, Y.; Li, J. Formation and
characterization of the XeOO+ cation in solid argon. J.
Am. Chem. Soc. 2006, 128, 2504-2505.
| www.editorialmanager.com/nare/default.asp